This invention relates to flow control apparatus for use in a vehicle roof top air conditioning unit for uniformly distributing the return air flow across the entrance face of an evaporator coil.
Air conditioning units that are mounted on the roofs of motor vehicles such as trailers, vans, motor homes, or the like generally passes conditioned supply air downward through a vertical opening in the vehicle's cabin roof. By the same token, return air is also able to be drawn vertically into the unit through a second opening in the cabin roof. Accordingly, the return air flow must be turned about 90.degree. before entering the evaporator heat exchanger and the conditioned air again turned 90.degree. upon leaving the heat exchanger before being discharged through the supply air duct. The routing of conditioned supply air is normally achieved by use of a centrifugal blower which is positioned adjacent to the exit face of the heat exchanger over the supply air duct. The blower is arranged to draw return air through the heat exchanger and pump the conditioned air downwardly through the supply air duct.
The blower arrangement is a relatively efficient means of handling the supply air. Routing return air through the evaporator heat exchanger is more difficult and typically less efficient. Turning the vertical incoming flow toward the entrance face of the heat exchanger within the limited space available oftentimes results in a non-uniform flow distributor across the evaporator, thereby adversely effecting its performance and that of the unit. In addition, vortices and turbulence can also be created in the flow which serve to block the return air flow to parts of the exchanger.